The invention relates to a method for producing an oil scraper piston ring, and to a piston ring.
Very high running surface wear on the running lands of oil scraper piston rings is observed time and again in certain engine projects. It has been found that high wear rates occur even with extremely wear-resistant running and coatings, which ultimately can only be compensated for by comparatively high layer thicknesses. Nonetheless, the ring must fulfill the requirements in terms of oil consumption and friction over the entire service life.
EP 1 409 896 B1 describes a method for producing an oil scraper piston ring, which is provided with a running land comprising a wear-resistant coating by generating, before the wear-resistant coating is applied, on the running land side, a profile which, in a conical region that forms both the outer circumferential surface and the running surface of the running land, has a radial elevation that protrudes radially outwardly from this conical ring plane, wherein at least this profile is provided with the wear-resistant coating, and wherein a predefinable amount of material is removed from the coating at least in the region of the radial elevation, so as to establish a substantially uniform running surface profile over the ring circumference.
WO 2008/151589 A1 discloses an oil scraper piston ring comprising a base body having a radially outer running surface, an inner circumferential surface, and an upper flank and a lower flank, the ring having at least two running surface lands, which are provided with a wear-resistant layer, if needed, and which, proceeding from the base body, are conically tapered at a predefinable angle, forming limbs, radially in the direction of the ends thereof facing a counter running surface and, proceeding from an oil chamber-side region, the free ends of the running surface lands being designed to be slanted in the direction of a combustion chamber-side region, wherein the respective transition regions from the slanted region of the running surface land into the limbs on the one hand, and from the limbs into the base body on the other hand, are rounded, which is to say provided with defined radii.
The running surface contour is a radius in this embodiment. The width of the bearing contact surface of the lands thus increases quickly as wear increases, resulting in increased oil consumption after a certain operating time.